Decreased neuronal death in Na+/H+ exchanger isoform 1-null mice after In Vitro and In Vivo ischemia

Abstract

Na+/H+ exchanger isoform 1 (NHE1) is a major acid extrusion mechanism after intracellular acidosis. Wehypothesized that stimulation of NHE1 after cerebral ischemia contributes to the disruption of Na+ homeostasis and neuronal death. In the present study, expression of NHE1 was detected in cultured mouse cortical neurons. Three hours of oxygen and glucose deprivation (OGD) followed by 21 h of reoxygenation (REOX) led to 68 ± 10% cell death. Inhibition of NHE1 with the potent inhibitor cariporide (HOE 642) or genetic ablation of NHE1 reduced OGD-induced cell death by ∼40-50% (p<0.05). In NHE1 +/+ neurons, OGD caused a twofold increase in [Na+]i, and 60 min REOX triggered a sevenfold increase. Genetic ablation of NHE1 or HOE 642 treatment had no effects on the OGD-mediated initial Na+i rise but reduced the second phase of Na+i rise by ∼40 -50%. In addition, 60 min REOX evoked a 1.5-fold increase in [Ca2+]i in NHE1 +/+ neurons, which was abolished by inhibition of either NHE1 or reverse-mode operation of Na+/Ca2+ exchange. OGD/REOX-mediated mitochondrial Ca2+ accumulation and cytochrome c release were attenuated by inhibition of NHE1 activity. In an in vivo focal ischemic model, 2 h of left middle cerebral artery occlusion followed by 24 h of reperfusion induced 84.8 ± 8.0 mm3 infarction in NHE1 +/+ mice. NHE1+/+ mice treated with HOE 642 or NHE1 heterozygous mice exhibited a ∼33% decrease in infarct size ( p<0.05). These results imply that NHE1 activity disrupts Na+ and Ca2 + homeostasis and contributes to ischemic neuronal damage. Copyright © 2005 Society for Neuroscience.